1. Field of the Invention
The present invention relates to drug delivery devices and, more particularly, to transdermal drug delivery devices (TDDD's).
2. Description of the Prior Art
Delivery of drugs transdermally has been in practice for some time and various devices have been developed for such purpose. Such known devices may be categorized as a reservoir device with a rate controlling membrane, a reservoir device without a rate controlling membrane, a monolithic system and a laminated structure. These devices are described in detail in Transdermal Delivery of Drugs, Volume I, pages 7-11, edited by Agis F. Kydonieus and Bret Berner, published by CRC Press, Inc., Boca Raton, Fla. Various patents have also been directed to transdermal drug delivery devices. In example, U.S. Pat. No. 4,286,592 is directed to a device having a reservoir for the drug to be administered. A contact adhesive layer in fluid communication with the reservoir serves in the manner of a conduit for transmission of the drug to an adhered skin surface. The adhesive layer equilibrates with the drug containing reservoir and determines the release rate for administration of the drug. Devices of this type generally provide a rapid initial administration followed by an asymptotically declining administration rate. For many drugs, such a varying rate of administration is unacceptable. In a monolithic type device the drug is disbursed throughout a carrier, layer or membrane in contact with the skin. In an adhesive dispersion type of device, the drug to be administered is disbursed throughout a layer of adhesive applied directly to the skin.
The delivery rate of the latter two types of devices identified above correspond closely with that of the reservoir type. That is, an initial rapid delivery rate exits which tapers, essentially asymptoically, over a period of time; the skin usually serves as the limiting factor of the absorption rate.
Transdermal drug delivery devices have been used for the delivery of scopolamine to counteract the nausea attenant sea sickness or motion sickness in land based vehicles. Generally, administration of this drug for a relatively short period of time and at an imprecise or unpredictable rate still seems to provide acceptable and beneficial results. For long term delivery of a specific drug, substantial control and regulation of the delivery rate may be of paramount importance.
Substantial literature exists to describe the difficulty with and low success rate of breaking the smoking habit. Some studies have concluded that the drug nicotine may be as or more addictive than most other habit forming drugs, such as heroin, cocaine, etc. Aside from the physical addiction that smokers may have, social and emotional dependencies attendant the manipulation of the smoking related implements and visualization of the smoke itself can constitute additional difficulties in breaking the smoking habit. Numerous experiments have been performed to explore the beneficial effects of transdermal delivery of nicotine as an adjunct to or in combination with a smoking cessation program. Although not conclusive, studies have indicated that transdermal administration of nicotine may be of assistance to a smoke participating in a smoking cessation program by segregating different aspects of the habit and thereby permitting therapeutic work on each such aspect.
Studies to date suggest that delivery of nicotine must extend commensurate with the normal smoking hours of a smoker. Furthermore, the delivery rate must be relatively commensurate with the depth of the smoker's habit. Without such near duplication of the level of nicotine to which the smoker has been accustomed, the craving for nicotine may be too overpowering to permit effective work on breaking the related aspects of the smoking habit. Irritant, mutagenic and carcinogenic hydrocarbon molecules, the secondary detriments attendant inhalation of smoke, which in fact may be more of a health hazard than nicotine, are not present during transdermal delivery of nicotine. Thus, a smoker has an immediate benefit if enabled to stop smoking even though the level of nicotine intake may remain essentially constant.